A number of artificial knee joints are known which are implanted as substitutes for the natural knee joints in the human body.
These endoprosthesis can be divided into two general groups. The joints of the one group make use of a relatively intact band or belt device and attempt, based on their construction, to permit as far as possible a physiological mode of movement. An example of such a knee joint endoprosthesis is shown in German Patent No. DE 39 22 294 (U.S. Pat. No. 5,123,928).
There are also known hinge type endoprostheses in which the femoral and the tibia parts of the prosthesis are connected with each other by a hinge joint. There is no need for a band device with these joints. They are most commonly used for heavily damaged joints, where it is consequently not so important to achieve a highly physiological mode of movement, but mainly just to make an implantation of an artificial joint possible.
The main problem with known hinged endoprostheses is stability. The hinge itself of the conventional joint endoprosthesis must bear all the resulting stresses, which occur during walking, from the tibia into the femur bone and vice versa. Also during load changes the hinge is stressed. In practice, this leads to problems of stability, namely to the tendency that the hinge pops out.
The purpose of the present invention is to develop a knee joint endoprosthesis for heavily damaged joints, which is strong enough to resist over an extended period of time all occurring stress, including load changes.